Asbestos is a commercial term applied to several minerals which are widely utilized, primarily because of their fibrous characteristics. All asbestos minerals consist of partially open bundles of very fine fibers, and most single fibers have a channel in the center. The principal asbestos minerals are chrysolite, crocidolite, amosite, and anthophyllite. Because they differ in chemical and physical properties, these minerals have different commercial applications.
Asbestos is "manufactured" by mining the ore deposits and separating the fibers from the non-asbestos rock. Some of the asbestos mines in the United States are located in California and Vermont. A number of other mines were closed in the 1970's.
Chrysolite is the serpentine variety of asbestos fiber. Chrysolite fibers occur in a wide variety of shapes. The idealized empirical composition of chrysolite is Mg.sub.3 (Si.sub.2 O.sub.5)(OH).sub.4. Variations in chemical analyses may be due to either associated mineral impurities or to isomorphic substitutions in the crystal lattice. Chrysolite, a hydrated silicate, is subject to thermal decompositions at elevated temperatures. This thermal decomposition is a two-stage reaction, consisting first of a dehydroxylation phase, and then a structure phase change. Dehydroxylation or the loss of water occurs at 600.degree.-780.degree. C. At 800.degree.-850.degree. C., the anhydride breaks down to forsterite and silica. These reactions are irreversible.
Because of its hydroxyl outer layer, chrysolite is readily attacked by acid and will, ultimately, completely dissolve the magnesium components, leaving essentially a fibrous but fragile silica structure. Similarly, because of its alkaline surface, chrysolite is not readily attacked by caustic solutions except under conditions of extreme alkali concentration and elevated temperatures. Chrysolite forms of asbestos comprise about 95% of the world's production.
All varieties of asbestos other than chrysolite belong to the amphibole group of minerals and are generically termed amphibole asbestos. The amphibole asbestos consists of two chains or ribbons based on Si.sub.2 O.sub.11 units separated by a band of cations. Seven cations form the basal unit. Two hydroxyl groups are attached to the central cation in each unit cell. These hydroxyls, unlike the chrysolite structure, are contained entirely within the amphibole structure. The final structure is composed of stacks of these sandwich ribbons. The bonding between these ribbons is rather weak, and the crystals are easily cleaved parallel to the ribbons along a cleavage line. If the cleavage is very facile, the result is an asbestoform mineral.
Amphiboles can also occur in nonfibrous forms which may result because of structural disorder. The dominant cations are Mg.sup.2+, Fe.sup.2+, Fe.sup.3+, Na.sup.30 , and Ca.sup.2+. Minor isomorphic substitutions of Al.sup.3+, Ti.sup.4+, K.sup.+, and Li.sup.+, also occur.
Like chrysolite, the amphibole asbestos fibers dehydroxylate and decompose at elevated temperatures. The presence of large quantities of iron makes the decompositions or thermal analysis determinations particularly complex and very dependent on the composition of the atmosphere.
The empirical compositions of crocidolite is Na.sub.6 Fe.sub.10 Si.sub.16 O.sub.46 (OH).sub.2. Crocidolite is the fibrous form of the mineral reibeckite. Crocidolite fibers, having an elliptical or circular cross section, are flexible and stronger than those of chrysolite.
The empirical formula of amosite, a yellowish-grayish white variety of asbestos found only in Transvaal, South Africa, is (FeMg).sub.7 Si.sub.6 O.sub.22 (OH).sub.2. Amosite fibers, which exhibit a rectangular section, are harsher and ordinarily slightly weaker than those of chrysolite. Amosite fiber lengths extend to 10-11 inches.
The empirical formula of anthophyllite is Mg.sub.7 Si.sub.2 O.sub.22 (OH).sub.2. If unexposed to the atmosphere, anthophyllite is a greenish-gray color. On being exposed to the atmosphere, however, it yields brownish-white fibers that are short and weak and are only slightly flexible. Anthophyllite is found in Georgia and North Carolina in the United States and also in Finland.
Because of their physical and chemical properties, the asbestos minerals are extremely useful materials, and are presently used in more than two thousand applications, including fireproof textiles, brake linings, thermal insulation, asbestos cement pipe, asbestos cement sheets, paper products, gaskets, woven fabrics, high temperature insulation, chemical-resistant filters, and filler material.
Recently discovered evidence indicates, however, that introduction of asbestos into living organisms increases the organisms' risks of developing various chronic diseases, including lung cancer, chronic fibrosing processes in the lungs, and mesothelioma of the lungs or intestines. The gravity of this evidence is underscored by the widespread applications of asbestos and the resulting frequent exposures of living organisms thereto.
Although it is not clear what happens when asbestos enters a cell, it is postulated that entrance of asbestos into living cells results in formation of ferruginous bodies, iron-containing protein bodies with a fibrous core thought to be formed by macrophage cells attempting to phagocytize a foreign fiber.
Ferruginous bodies formed in living organisms appear to occur in various shapes and sizes, including evenly distributed deposits, series of clump-like deposits, and large barbell-shaped deposits. Although sizes vary, the fiber core approximates the lengths and diameters of asbestos and other fibers found in living organisms.
It is further theorized that formation of a ferruginous body in a living cell occurs by depositions of ferritin, a crystalline iron-containing protein and/or hemosiderin, a yellowish-brown granular pigment formed by the breakdown of hemoglobin and composed essentially of ferric oxide, on an electronegative surface, such as the nucleophilic silicates present in asbestos fibers. The formation of ferruginous bodies in a living organisms appears to set in motion a collagen synthesis ultimately resulting in chronic fibrosis and a potential for developing carcinoma.
A number of prior art workers have sought to treat asbestos so that it is no longer an environmental hazard, with a variety of successes.
Roberts et al., in U.S. Pat. No. 4,678,493, disclose a method for vitrification of asbestos waste to render the asbestos inert. The asbestos is introduced into a body of molten glass at a temperature above the decomposition temperature of asbestos, along with a melt accelerator which may be an alkali metal compound, an alkaline earth metal compound, a fluoride, a chloride, or a slag such as blast furnace slag. The melt accelerator causes the asbestos to dissolve completely in the glass to produce a homogeneous glass. The crystalline structure of the asbestos does not appear to be changed, the asbestos merely forming a homogeneous mixture with the glass. The composition may contain up to about 80% asbestos.
Richter, in U.S. Pat. No. 4,808,198, discloses a method for rendering asbestos wastes harmless by altering the physical form of the fibers by melting the asbestos and by incorporating the molten asbestos into the slag phase produced by the partial oxidation of ash-containing liquid hydrocarbonaceous fuel and/or solid carbonaceous fuel.
Karstetter, in U.S. Pat. No. 3,585,054, discloses a method for chemically altering at least a portion of the crystal phase in a glass-ceramic article containing oxides of magnesium, aluminum, and silicon in the crystal phase which comprises bringing the glass-ceramic article into contact with a material containing an exchangeable lithium ion to effect an exchange of magnesium and lithium ions and the consequent development of lithium aluminosilicate type crystal phases.
Flowers, in U.S. Pat. No. 4,328,197, discloses a method for treating asbestos and other silicate minerals to minimize their harmful properties by forming a metal-micelle silicate by contacting a silicate mineral with an aqueous solution of a weak base, strong acid, or strong base-weak acid salt of manganese, chromium, cobalt, iron, copper, aluminum, or mixtures thereof.
Ikeda et al., in U.S. Pat. No. 3,425,817, disclose a method for lowering the melting point of glass by using a low melting point glass of PbO, B.sub.2 O.sub.3, and TiO.sub.3 with a high melting point glass of Al.sub.2 O.sub.3, SiO.sub.2, and Li.sub.2 O.
Chevalier-Bulktel, in U.S. Pat. No. 4,476,235, disclose a green molded product for preparing shaped units comprising 55-99% by weight of non-calcined asbestos tailings, at least one of a heat-decomposable metal salt selected from the group consisting of sodium, potassium, lithium, calcium, barium, magnesium, aluminum, and mixtures thereof; a natural aluminum silicate; and mixtures of the above. The serpentine asbestos is said to decompose during the firing process, losing the water of crystallization at about 700.degree. C. and being transformed into a ceramic body at about 800.degree. C., forming forsterite and enstatite.
Pundsack et al., in U.S. Pat. No. 3,304,197, disclose a process for modifying the surface of asbestos by treating the asbestos surface to make it organophilic. This treatment is solely for the purpose of making the asbestos more dispersible as a filler in organic matrices.
Kroyer, in U.S. Pat. No. 3,073,708, discloses a number of fluxing agents which can be used to reduce the melting point of glasses.
Dumesnil et al., in U.S. Pat. No. 4,743,302, disclose a low melting mass made by incorporating bismuth oxide, zinc, barium, or strontium oxide; and phosphorus, niobium, or tantalum oxide to a lead-vanadium-oxide glass.
Natale, in U.S. Pat. No. 4,705,429, discloses a method for disposing of hazardous asbestos waste material comprising depositing the waste material containing asbestos in an open pit of an underground shaft mine. Soil or mining tailings may be used to cover the waste material.
Crossley, in U.S. Pat. No. Re 15,727, discloses a method of using waste asbestos by heating a mixture of asbestos and glass to a temperature below that at which the asbestos begins to effloresce to form a solid solution. The solid solution is raised to a higher temperature to form a glass.